randomly high idle?

[jpc]

My '85 MGMCP with CFI usually idles OK. Occasionally it idles real high when the engine is warm.

Where would you look to debug this?

Also, on some cold starts, I need to give it a tiny bit of throttle to get it to start. This trick always works, and as soon as it starts I can take my foot off the throttle. Could that be related to the high idle issue? Is it a clue, Scooby Doo?

[1987cp]

CFI does supposedly have a mechanical fast idle cam like a carb does. Depressing the throttle would set the fast idle, which would then come off in response to a thermostatic control similar to a choke pull-off.

[shorty]

FIRST THING MAKE SURE FAST IDLE SCREW IS BACKED OFF (RED NEXT PIC) BEFORE YOU SET CURB IDLE. This is your idle control, first step, set to 550 rpm in drive WARM ENGINE, adjust bottom screw (green)
top (green) is idle stop this should move out when you wot the throttle and move back slowly

this is fast idle only ! cold engine
first step disconnect vac line (purple)
make sure cam is on bottom step (yellow)
make sure choke pull off is off (pink) all the way out
hook up tach and adjust screw (red) to 2000 rpm
done re attach vac line (purple)

here's a better pic of choke pull off and cam on fast idle

this is where i set my choke t-stat works great
when i start car i turn key forward till pump comes on then push pedal once and turn key to run this sets the high idle and also sends gas to the injectors
hope this helps

[jpc]

Thanks shorty for the hints...

I'm going to call this unintended acceleration (UA). That's the symptom, the car takes off on its own while driving.

First I tried lubricating the fast idle cam. The fast idle and thermostatic pull-off seems to work fine. On a cold start, the car goes to fast idle, and after 20 or 30s it kicks down to low idle. Great. Then the car drives fine, runs well, sounds good, pulls along nicely, everything seems A-OK... until about after 5 minutes of driving. Then the car starts to drive on its own. On a level surface, it will maintain 35 mph with no accelerator pedal input. Yikes.

If I shift into neutral, the engine will rev up, not super high, but medium speed. Then if I press the accelerator and let off, often the revs will drop, though not quite as low as a normal low idle. Ford saved a few dollars by not equipping this car with a tach so it's not easy to quantify this.

When the engine is fully warmed up there's no problem. The UA only seems to happen at about 5 minutes of driving after a cold start. It will go on for a minute or two and then vanish.

The second thing I tried after lubricating the fast idle cam was to back off the fast idle adjustment screw, so that fast idle isn't very fast at all. This makes a difference when starting cold, as you'd expect, but it doesn't seem to change the unintended acceleration behavior at all.

Where would you look next?

This car has working cruise control. Somewhere there must be a cruise actuator attached to the throttle cable. If it's possible to disconnect that, I may try that, and see if it makes a difference.

[ford man]

Yes I would disconnect the cruise control cable... It rides on top of the accelerator cable and you can pop it off with a flat head screw driver.

Don't let this happen to that beautiful wagon...



To sum up the Dateline story, the Ford cruise always has power to it even if you never turned it on and if it shorts out or two contacts touch it can go wide open throttle without warning!

Also: maybe the TPS sensor?

[ford man]

You can see the cruise control in Shorty's first picture: the black plastic thingy; take that off...

Also: Idle step controller?(the round motor that pushes on the throttle linkage, in the same picture)

[jpc]

So that's what the black plastic thingy is.

What does the idle step controller do? I fiddled with the idle step controller and its motion was not smooth. That could be it.

How would a TPS sensor cause acceleration? Does its reading feed back into the idle step controller or the fast idle cam?

Time to read the service manuals...

[shorty]

So that's what the black plastic thingy is.

What does the idle step controller do? I fiddled with the idle step controller and its motion was not smooth. That could be it.

How would a TPS sensor cause acceleration? Does its reading feed back into the idle step controller or the fast idle cam?

Time to read the service manuals...

take off air cleaner housing so you can see fast idle cam. start cold and watch the cam and pull off make sure
pull off and tstat keep high idle cam off let my know what happens try and take some pics of cam set cold and warm

[shorty]

choke pics cold and warm up
1 pic engine cold choke not set
2 pic push pedal once set choke
3 pic choke pull off after about 30 sec or so
4 pic choke all the way off after tap on pedal

[stucknsask]

i just watched a video on you-tube about the fuel pressure regulator leaky diaphragm
while searching for a reason for my crank, crank, crank, no start issue, and realized
that just maybe this was my problemo, as the rubber diaphragm can tear or rupture and and spew extra fuel causing all kinds of problems, even fires; when it totally ruptures;
a good video to watch ; link

http://www.youtube.com/watch?v=AKtR_yF7bi8&feature=related

i couldn;t remember were the real bad video was but is shows a steady stream of fuel
leaking when it totally ruptured;

hope this helps...

[jpc]

Okay, I think that my throttle cable is toast. Has anyone had good experience with a replacement product?

Autozone comes up with a Spectre 3 ft. universal throttle cable kit. This concerns me. Universal means not tested on your car. Kit means it comes with multiple adapter brackets, one of which must be creatively deformed to fit your car. And Spectre? Really? The car already ghost-drives. That's the problem!

To diagnose it, I unhooked the throttle cable and cruise control cable from the throttle body, and from each other. The throttle moved smoothly and returned without hesitation to the same closed position each time, with the TV linkage and fast idle gizmo attached. The cruise control cable moved freely and smoothly. Nothing makes me think the cruise control was somehow being activated a la Dateline NBC. The throttle never opened on its own and never went near WOT.

The throttle cable does NOT move smoothly. It hems and haws and catches at certain places. After playing with it for a couple minutes, it smoothed out. That's exactly how the car drives, misbehaving for a couple minutes before acting like nothing ever happened. The factory service manual says you can't lubricate the throttle cable, you must replace it.

[jpc]

Okay this looks less universal and more like the actual OEM part:

NAPA accelerator cable

This too.

ebay

[ford man]

Just hit everything with carb cleaner to free up your throttle linkage. Sounds like your throttle cable is fine. You might check your Tv rod return spring returns the rod quickly and I recommend replacing the plastic tv rod bushing with a copper one.

I wasn't suggesting that the cruise control was the root of your problem just that you MIGHT want to leave it disconnected if you don't use it.

I put some zip ties on my throttle cable where it attaches to the gas pedal because it was slack and I wasn't getting full throttle travel. Not related to your problem just a pro tip.

[jpc]

Cruise control is not the problem, the car ghost-drove today with the cruise cable unhooked.

I managed to get a look under the hood when the throttle was sticking open. Finally!

The idle step controller wasn't contacting the paddle on the throttle wheel. I don't think that was a factor.

Then I shut off the motor and found the fast idle cam wasn't at the lowest step. Aha.

So I'm thinking the bimetallic strip might be unreliable, it may be engaging the fast idle even after the car has been warming for a few minutes. Is that likely?

For now I backed the fast idle speed way off so it's safer to drive.

The TV rod returns quick and smooth. The whole throttle and linkage seems to turn smoothly and return with no hesitation.

So I am thinking I should replace the scratchy-feeling throttle cable and the heating element/bimetallic strip gizmo on the fast idle cam.

[shorty]

This is what went wrong with my car as well, part number from rock auto
STANDARD MOTOR PRODUCTS Part # CV237 Choke Thermostat $16.48 rock auto

check pic 4 post #3 of how i set thermostat, works great